A peptide containing immunoreactivity to the amphibian peptide bombesin was isolated from bovine milk. The isolation procedure, however, gave relatively poor yields in spite of the precautions taken against loss due to absorptivity on the walls of various containers. New procedures are being developed to increase the yield of peptide recovered and decrease the number of steps in the scheme. Amphibian and mammalian bombesin-like peptides are known to affect gastric secretions either by i.p. infusion of the peptide or by intracerebral ventricular administration; a bombesin-like peptide in milk may have a similar mode of action. Thus, a preliminary assessment was under taken on a large number of potential analogues of milk bombesin on their neuromodulatory role of gastric secretion in rats. The data can be summarized as follows: (i) Trp in position 8 is required for biological activity; (ii) Gln and His at positions 6 and 12, respectively, are also important; and (iii) and unknown extension of sequences preceeding Gln6 are involved since neuromedin C (GRP 18-27) appears inactive.